1. Field of the Invention
The present invention relates to the development of electrographic images and more particularly to apparatus for developing electrostatic images with single-component, conductive toner.
2. Brief Description of the Prior Art
It has been disclosed in the prior art that conductive toner particles, in contact with an electrostatic image-bearing member and provided with an electrical path to ground, will develop an induced charge, opposite to the image charge, and develop the electrostatic image (see, e.g., U.S. Pat. No. 3,166,432). One structural mode of implementing this development technique has been to feed such an image-bearing member into and through an electrically-grounded tray containing a supply of the conductive toner particles.
One problem which exists in such apparatus is that objectionable background toner deposits are caused by the intimate contact of the image member with toner in the bath. That is Van der Waals or other similar forces can cause toner deposition in uncharged areas, and electrostatic forces create similar problems in incompletely discharged areas. However, such prior art systems suffer an even more serious limitation in that no reliable control has been provided for establishing a threshold of development relative to the electrostatic images. Such a threshold is useful to control unwanted background depositions, but additionally, facilitates compensation for changes in system parameters, e.g., as might be presented by original document of differing background or image densities.